The present invention relates to power supplies for providing a plurality of output voltages. More particularly, it relates to a single DC power supply which splits an input voltage into a plurality of output voltages.
Many electronic circuits require operating electrical power at more than one voltage level. For example, circuits using operational amplifier devices often require +12 and -12 volts supplies. Conventionally, two completely independent power supplies are provided. This is, however, expensive and often impractical because of the input voltage available to the power supply. One alternative when a simple input voltage is present is use of a resistive voltage divider circuit has been used to split an input voltage into dual output voltages. The voltage at the divider network common node establishes a reference voltage. Under load, the reference voltage can change, thereby shifting the operating bias point of the supply and rendering the split voltage unequal. The shift can be reduced by making the resistor values smaller. But, low resistor values are often undesirable because the load on the power supply is increased and energy lost. There can also be degradation in common mode rejection of operational amplifiers in the circuitry being supplied with operating power. Also, increased noise in the power supply can result.